A widely used type of rotary wafer switch has the following construction. A plurality of wafers which are approximately rectangular and which each carry a plurality of contacts arranged in an annular fashion are mounted parallel with each other transversely across the interior of an aluminum alloy wafer housing which is U-shaped in cross-section (the bottom of the U being flat) and which is substantially longer than it is wide. Co-operating with each wafer there is a circular contact carrier which carries one or more movable contacts and all the contact carriers are rotatable together by means of a common shaft which extends longitudinally of the housing through all the carriers. At one end of the housing there is mounted an indexing mechanism which has an operating knob for turning the shaft. At the other end of the housing there is an end plate which serves to keep the two side walls of the housing tied together at that end. The indexing mechanism serves to define a plurality of different angular positions to which the shaft may be set, thereby setting all the contact carriers to corresponding positions. In the different positions, the movable contacts on the contact carriers make contact with different ones of the fixed contacts on the respective wafers. The fixed contacts on the wafers are connected to terminals on the wafers so that a multitude of electrical circuits connected to these contacts can be made, or broken, in various different combinations depending on the position to which the switch is set. It is believed that the operation of the switch need not be described further since it is very well known in the art.
As regards the switch construction, each wafer has applied to its opposite edges an insulating plastics member. Its contact carrier is then secured adjacent the contact-carrying face of the wafer. This sub-assembly is then positioned across the interior of the wafer housing, which is slightly spread at this stage to facilitate insertion of the sub-assembly and normally several other similar sub-assemblies at the same time. The side and bottom walls of the housing have holes in them and the insulating pieces on the edges of the wafers have corresponding projections which fit into the holes. When all these sub-assemblies have been placed in position they have to be held in position while the side walls of the housing are squeezed inwards to firmly engage the insulating pieces and thereby properly locate and retain the wafers. The insulating pieces are required between the wafer edges and the housing because conductive paths on the wafers come quite close to the wafer edges and there would otherwise be a possibility of short-circuiting inadvertently occurring between these paths and the metal housing.
As regards the movable contact carriers, these are such that once the contacts have been inserted in them and the carriers have been secured to their wafers to form a sub-assembly, the contacts can no longer be removed from them. Consequently, once the whole switch has been assembled it will have to be completely dis-assembled if it is then found that one or more of the movable contacts in one of the contact carriers has been mis-positioned.
It will be appreciated from the above that assembly of the prior art type of switch is not simple, the number of parts required is quite large, special tooling is required for efficient assembly, and the rectification of any mistakes made in inserting the movable contacts requires complete dis-assembly of the switch.